I'll never forget being told by an older coworker when I was in my early teens. "Don't sweat the small stuff. And it's all small stuff".  Not that I totally agree, but it's a good heuristic to live by IMO. 

 Also, don’t smell the sweaty stuff. 

 I always heard. “Don’t sweat the petty things; and don’t pet the sweaty things.” 😂