First, you need to learn a little brush anatomy. You've heard about icebergs and how the bit that sticks out is just a tiny bit of the whole thing, right? The bristles on a brush are the same way. Most of the length of the bristles goes down into the neck of the metal ferrule. The secret to virtual brush immortality rests in not letting your Paint  get up into that ferrule. If any Paint  at all manages to dry in there, it will stay there forever. If it builds up, it l will force the bristles apart, causing the brush to splay apart. Once this happens the brush is dead,  unfixable. I did not know this rule when I had my first brushes, they were a set of Hamiltons beautiful bristle brushes ,till I got my hands on them..i had spent so much time as an apprentice cleaning out Brushes, pots, rollers, cups, trays all manner of things apprentices had to do ..Oh!! and make  a good Brew..  so I got lazy when it came to my Brushes,till the day I had let my brushes go hard overnight...  I had been going somewhere ..the following morning .... They were dead!!  no amount of reviver would bringing them back from beyond.

"Where is your kit lad" the foreman asked ..err.err! he picked them up looked at me..looked at the brushes and  threw the brushes in the bin.."No Tools No Work" I was  sent  home ....