When it comes to skills like tennis, math, piano, you can improve at them the more you work at it, the more hours you spend, the more focus you bring to the path you take to the goals you’re trying to reach. If I concentrate harder, I get results faster, because I’m controlling myself more, and success is gained when I can perform and execute the technique perfectly. The more time I spend, the more practice I get, and the more likely I am to execute the technique perfectly. This ability to learn and learn quickly is very important in life, and is typically how people ‘succeed’ in the objective and competitive sense of the word.
Then there are things like relationships where your results improve when you’re not working at it, that don’t improve solely based on the hours you spend on it, and where focus can actually reduce your success significantly. A relationship is successful if they remember you when you’re gone, not that they pay attention to you while you’re there. Spending time alone doesn’t improve the relationship, spending quality time does, and there’s only so much quality time available per day and interaction before it becomes suffocating to spend more time together: overstaying results not in diminishing returns but actually in negative returns. Spending too much time weakens the relationship, not strengthens. And focusing too hard on someone is creepy, and so leads to failure.
Applying the skills used to master skills to relationships will lead to failure. Separate the two, and develop a well rounded toolkit. Be able to learn quickly, and also be able to improve relationships.