From Longman Dictionary of Contemporary Englishsomething is not for the faint-heartedsomething is not for the faint-heartedDIFFICULTused humorously to say that something is difficult and needs a lot of effort → faint-hearted
Examples from the Corpus
something is not for the faint-hearted• Playing foreign markets is not for the faint-hearted.• Well, starting your own business is not for the faint-hearted.• Litigation is not for the faint-hearted - or the half-hearted. 