My comprehension over this saying is that it depends.
The premise is that it comes to affairs involving friends, or in other words, you claimed each other to be true friends, not only classmates, colleagues, etc..
1. If a person had done or is going to do bad things, he should not require his friends' help.
2. If a person had the ability to offer help when his friend was once in need but he did not, he should not require this friend's help when it is his turn to be in need, and it depends on if his friend is willing to help him then.
3. If a person is in need out of the cases discussed above, I hope that he can receive help. At least the phenomenon "kick Jimmy when he was down" would not occur.
4. We can not compel a person to help another one.
But I have seen a lot of occasions where there are people of the first and second group blaming their friends for the reason that the friends didn't help them when they were or might be in need. What's worse, the occasions lead to revenges sometimes.
It will be tiresome to argue with those people... Sometimes good mottos, adages, etc. are used by them in a unimaginable way to complaint about others unjustly.
What‘s your opinion?
Updated at 4:32pm Beijing time.
Seth might be correct regarding the alternate meaning, but I was taught it means the following. When you are in serious trouble (the kind of trouble that scares off a fair weather friend) and you are in need of some help, a friend who is willing to help you out is indeed a true friend.
For example, if you were falsely imprisioned in a foreign country, a true friend might bring lawers, guns and money and get you out. A fair weather friend might pretend he doesn't even know you.
Something in high demand is something precious to be needed. So be that.