Not quite les,
Pluck for going mountain climbing in the first place
"Pluck" = fortitude, "for going" gives titude
"Mountain climbing in the first place" as you correctly say Les; alp "climbing in the first place" gives pla placed first. So pla + titude.
"Its a cliche but you'll need" is the definition and a preamble. Me/I normally in a clue referring to the setter so you = the solver.