I'm normally quite in favor of stretching your mind in any direction — but allowing some thoughts to exist, and especially to settle in and become habit, is downright poisonous.
These thoughts are the harbingers of feeling and getting old, of being stuck in a rut, of allowing unhappiness and regret and dissatisfaction to run your life into the ground. Train yourself to see a giant red flag whenever any of these thoughts come up, and respond to it by jumping up and doing something, anything, different. Never ever indulge in these, in either the sense of letting them become your underlying beliefs (if they do, root them out and burn them), or letting them guide your actions. Here be the real dragons:
1. I can't / won't do that because I'm not good at it.
The fastest way to get old, boring and miserable is to allow yourself to see the point of doing things as *product*, rather than experience. Learning new things, branching out, making art for the sake of making it, and staying happy and engaged with life all require that you do things, not even if you aren't good at them, but ESPECIALLY if you aren't good at them. You learn, grow, and feel more when you engage with things you haven't encountered, or don't have a natural aptitude for. The more experience and aptitude you get, the more things you aren't good at you should be seeking out. When you're a kid, finding things you aren't good at to try and work on is easy, because it's most things. When you're older, it's imperative that you aren't shy about looking for more.
2. Let's not go there; it's scary.
Growth is scary! Intimacy is scary! The unknown, which is absolutely required to improve anything, is scary! There's a difference — a stark one — between the good-adult skill of recognizing when a risk isn't worth it (hmm, I *could* run naked down this alley with money glued to my limbs, but would that actually be a worthy trade-off?), and the death-rut of letting yourself pull back from things because they invoke feelings you don't understand or are intimidated about experiencing.
You know what's the most terrifying thing I've ever done with my life? Nope, not deep-water breathholding; not winter camping with no cell phone; not hanging out in Detroit; none of that. The scariest shit I have ever beheld or put myself through was all about letting myself love, and be loved. If I let myself think "we ain't doing this, it's scary", then my life would be lacking some of its best experiences. All the really good things are scary. Scary is NOT a reason to not do something: In fact, if you're the more advanced type of grownup, it's a damn good reason to consider it.
3. I'm too ugly to.
No you're not. Just no. The problem is never what you look like — never, ever, ever. The problem, if there is one, is how comfortable, and able to love and appreciate, yourself you are. If you ever feel too ugly to do anything, realize that it's a symptom of a problem all right — and one that has nothing to do with your face, hair, body, fat, massive scarring, missing limbs, or any of that.
The vast majority of us get uglier as we get older. Fortunately, many of us also learn at the same time that being ugly is the tiniest blip on importance-radar, in almost everything. If you're really exceptionally ugly, or really exceptionally not-ugly, then this will change the dialog you get from some of the NPCs in life, at least initially. But whether you're confident, whether you love yourself, and whether you can stick your flaws out there (because you have them now, and you'll have more later, no matter who you are), this matters in the utmost.
As much as you can, take no shit from your own brain about being ugly, and never let it convince you that your looks make the difference between whether you can do a thing or not. Whatever you're doing, at any age, your attitude and your degree of self-love matter a million times more. (And yes, I also mean sexy things. I have personally seen many an older, technically-ugly person rock the shit out of a highly sexualized activity while a visually-beautiful person had all their spark snuffed by self-doubt. Sexiness, as most people learn at some point (though some too late), has very little to do with what you look like. The eyes are one sense among many that come into, well, play. :D)
4. I'm full.
I don't mean of food — I mean of experiences, knowledge, and living. I often wonder if the injunctions against gluttony in Western religious traditions are in some way related to, or a misinterpretation of, the injunctions in Eastern religions (where, you know, Fat Buddha is a thing) against being "too full" for life to give you anything. (Watch this scene from the Forbidden Kingdom if this concept is not familiar.) People who feel like they have nothing left to learn are, frankly, dead already. And I'm not ashamed to admit that adults who give off this vibe — it's getting easier and easier to find them at my own age, especially in ye olde professional realm — scare the shit out of me. "I'm done; I've finished (whether interpreted as having won or lost); life has nothing more to teach me here" is one of the most corrosive thought-patterns to everything good I've ever seen in the world….::shudder::
5. I get it.
This is the "nothing new under the sun" problem. It's related to the last one, because it's a type of declaring "nope, I'm full"; only it's a bit different, because it's even more arrogant and destructive. Instead of just declaring "life has nothing more to teach me", you're declaring, "there is nothing more; I am not only full myself, but I am full of all there is, and there is nothing more to this topic than that which I already know". Often the resulting emotion in this case is despair — because what else could you feel, if you really believed that you'd done and thought and experienced everything there was to do in the realm of love, or adventure, or whatever?
I don't feel like I need to necessarily argue that anyone stuck on this type of thinking is wrong — if you're not stuck in it yourself, that seems obvious. But even though it's obvious that it's not true when you aren't feeling it, it can be deadly when you are, so again, please add it to your list of things-that-throw-a-giant-red-flag-and-should-be-killed-immediately.
Happy new year and whatnot, ya'll. Hopefully all these useful thoughts I'm having will help me pull myself up and set a good path forward in the wake of this incredibly challenging couple months. Good luck to all of us!