Many people are very patient never get tilted and leave all their roll on poker sites and do exactly what blix177 said good advice by him I agree if you got serious discipline.
But will be honest as I have tilted before going from playing freerolls and $20 tournaments calmly to suddenly after few beats playing $50,$100,$250,$500 and even $1000 buy ins chasing a break even or slight profit in a session when I left large rolls online in the past with disastrous consequences.
These days if have a decent 4 digit roll for example set aside for poker I try to keep it off the poker site feed smaller rolls into the at risk blender reload and withdraw regularly take a few shots when fresh feeling calm and relaxed at the higher stakes make it impossible to have a 2k or 5k downswing in just one session.
Leaving smaller rolls on poker sites instead of big ones freerolls mentally are easier to play and keeps you focused and hungry and concentrated in the micros and midstakes.
Loose play and bad BRM buy in decisions with big rolls and profits making mistakes can be a serious leak too in a players game that I try to control by withdrawing most of it instead.
Poker sites regularly hit zero for me due to my aggressive withdrawal strategy but I never hit zero with my bankroll reserves ready to deposit if this makes sense.