On the contrary, I'd argue that it's not true in specific cases.

"Because it's hard" is a cop-out.

"It's too hard to accomplish given constraint [X]" where X is a deadline, financial constraints, or other real/tangible resource limitations might be one thing. But if you're working on your own timeline on some sort of open-source project, or there is nothing external preventing you from acquiring the expertise/resources to conquer the hard problem, then "Because it's hard" is an absolutely shitty excuse to not do something.