MacBook shows folder icon with Question mark on boot up still boots fine

Just this morning when I booted up my MacBook, I noticed the infamous folder icon with a question mark flashed up on the screen once, then the normal apple icon appeared and the computer booted normally. I ran Disk Utility, Disk Warrior, Hardware Check, etc. and found no errors.

First, I'd like to know if this is anything catastrophically wrong with my computer. Regardless if there is or isn't, secondly, I'd like to figure out how to stop this from happening.

Thanks.