Studying: Strengths vs Weaknesses
**Opinions are based on my observations over the last 12 years, your mileage may vary**
There are essentially two ways of getting better at anything in life.
1. Bolstering your strengths
2. Reducing your weaknesses
This has some really interesting implications while improving your chess. When you are still a relatively lower-rated player (we'll say <1400), you only actually need to do one or the other and you can climb the ranks. Most players choose to bolster their strengths at this stage - studying openings to catch their opponents in a trap, etc.
However, once you rise above this stage you inevitably hit a plateau where your weaknesses overshadow your strengths and you consistently lose games you thought you were in good shape in against players of your own level. Why? Because as you climb up your strengths and weaknesses become more specific. At 1200, you might consider a weakness to be endgames. At 1600 your weakness is less likely to be endgames in general - it may be R+P endings.
This leads to an interesting shift at more middling ratings (1400-1800) to shift to reducing weaknesses. So now you are 1900, but you can't seem to win games at your level. You aren't losing due to your weaknesses, but your strengths haven't caught up to that level such that you can consistently win.
Now we're back at time to bolster strengths. However, now it isn't enough to know how to win a piece with a two-move tactic. Now you also need to know how to execute a tactic to give you a lasting initiative or control over a key square.
The progression continues with strengths and weaknesses getting more specific the higher rated you end up. Both improving your strengths and minimizing your weaknesses are needed to get significantly better at chess.
Do you work more on strengths or weaknesses when you study? Do you study more broadly or deeply?