You shouldn't be afraid to lose your BR because you shouldn't have your full BR at risk.
Play with bankroll management. For MTTs, have at least 100 buy-ins at a certain level to play with to start. Depending on skill level or how comfortable you are, you can choose to decrease/increase the buy-in range. I wouldn't drop below 50 buy-ins and going over 200 buy-ins is a bit excessive, but totally fine if you're more comfortable with that.
Don't think of it as money either, but as buy-ins. If you have a $100 BR and are playing .50-$1 MTTs, don't think of it as losing $1 here or $10 in a week of playing, but look at it as 1 buy-in or 10 buy-ins. Or as investments. In order to win an MTT, you need to make a small investment in order to earn a big pay out. No investment, no payout.