Yes, you can be smart and bad at chess at the same time. Being smart doesn’t automatically give you a special talent at chess. It just means you have the potential to be good at it. No matter how smart you are, you will still be bad at chess without practice, learning, and some dedication.
Bullet chess can make you better but only when played with regular, slow chess too. If you only play bullet chess, you will get better at bullet only. You could lose the ability to put deep thought into the ordinary chess game and if you encounter a pattern on the board that you don’t recognize, you will be floundering. Bullet chess can be great for practicing time-poor end games.
The difference is that a chess strategy is the long-term overall plan for your game whereas your chess tactics are the individual sets of moves that you use to achieve an objective as part of the game. Strategy is the bigger, wider view of the game while tactics are a closer, zoomed-in look at certain moves.
4 or 5 focused games a day are better than 20 quick wins. If you are playing with the specific intention of becoming better at chess, then it is a good idea to play fewer games every day but with a higher level of effort and against a stronger player. This is better than playing lots of short, easy games for a couple of quick wins.
Most people are bad at bullet chess because they’re afraid to make a move, they haven’t memorized enough game patterns, or they simply don’t enjoy high pressure situations. This is OK, because there are coping tactics for bullet chess players or you could just play regular chess.
You can certainly learn chess at 30 or older. It’s never too late to learn, study, enjoy, and play chess. Unlike physical sports there is no particular barrier to entry with chess as you grow older. It takes a focused approach and a sharp brain, which is possible at any age.
Chess puzzles are very useful if you are looking to train your tactical aptitude. Beginners will learn a lot from setting up situations and then analyzing them to get the specified outcome. There are limits to the use of puzzles, however, because chess is not just tactics; it can be hard to recognize a situation without “puzzle language” or the hints offered at the beginning of puzzles.
Chess is so complicated because there are 6 different pieces replicated in various amounts to make 32 in total, and they are allowed to move on a board of 64 squares. This makes billions of possible positions and an infinite number strategies that can make use of them. Chess being complicated is a good thing too: It means that no one can learn all the possible outcomes so playing chess will always be interesting.
Chess coaches are worth it because they can quickly elevate your skill level. The right coach for the right student can make a huge difference to the quality of game they play.
You’re probably not “suddenly” bad at chess. You’re probably having an issue of focusing on your game for a few days. Maybe you’ve convinced yourself that you’re going to lose anyway, and that’s a great way to lose confidence.