For me, as there are so many "variables" when soldering, the most difficult thing is knowing what's wrong.

For example, you end up with a poor soldering. You try again, and again, but it doesn't get better. Maybe only worse. But what was wrong?

- Was the temperature OK? (And is my iron reporting the real temperature? Should I spend another 300 bucks in a soldering tip thermometer?)

- Maybe the solder I bought is not appropriate?

- Was it the flux? Did I apply it correctly?

- Also, is this tip the best one for the job? Besides, I could have damaged it before when trying to solder and it's not good anymore, although looks good to me

- Or my technique isn't good enough. Am I drag soldering this right? Maybe I should apply heat for longer? But what if I damage the component?