Okay, here's what I want to talk about. Instead of specifically a piece of bad advice, I want to talk about useless advice that isn't really advice at all.
"Just let it go"
"Why are you letting that upset you"
"You shouldn't be devoting attention to that"
"Be the bigger person"
"There are more important things to worry about"
Those. Those kinds of things. They are not "advice" and though people who say them think they're helping, you need to understand those are not loving statements. They are DISMISSIVE statements. They are statements designed to make someone think the only problem here is that someone feels incorrectly or inconveniently about something that is affecting them.
Yes, some people are better at coping with stress or disasters than other people are. I actually tend to be pretty good at such things myself. But when I'm angry about something, or I'm having a problem that someone else doesn't really understand, I am VERY VERY SICK of telling someone whom I expected to be sympathetic only to be met with a statement like one of the above.
It doesn't happen often. And that's probably because once someone says something like this to me, I know I can't trust them to respect my experiences. But just in case you who is reading this are a person who says things like this to people, I want you to understand why it is inappropriate.
You are reacting to someone expressing their feelings by telling them their anger or their passion is the problem. You aren't listening to why it's a problem, and you aren't coming into the situation with respect for the possibility that maybe they are outraged due to something outrageous. Or maybe they are not even "upset" or "worried"; they are perhaps venting, or helping YOU understand a stumbling block, or telling you about themselves, or trusting you to help them shoulder a burden. If you respond by telling them their reaction is more of a problem than the problem, you're derailing, and you're also being a jerk.
Don't tell other people to suck it up when they tell you about their problems. Being shamed into believing their reactions are inappropriate is awful. Being told the things they care about aren't very important because you don't share their concern or you think their problems are small does not encourage them to deal with the issue constructively.
IF YOU CAN'T HELP BUT THINK THEIR PROBLEMS ARE SILLY, the kindest thing you can do is just listen. I can't tell you how many times I've seen someone search for compassion only to receive condescension. Do not imply their problems aren't problems. Do not imply they're upset because they're "letting" something bother them. Do not imply that they should fix the issue by feeling differently about it. Especially since chances are you're saying that because you don't want to deal with their emotions.
The WORST advice I ever get is almost always unsolicited and is almost always a laughable corruption of where the problem even is. Don't be the kind of person who does this. I can assure you that if you ever talk like this to me, my willingness to trust you will be extremely limited unless you demonstrate that you've learned why it's unacceptable.