As always when you ask a lawyer a question, the answer is “it depends.” So what does it depend on? No litigator ever wins every case and judges, lawyers, etc. understand that you don’t get to choose the facts of your case; someone is on the losing side of every case that goes to trial. That’s what makes settlement attractive and what makes litigation fun for me.
But after our first meeting I’ll try to give the client an assessment of the odds: 1 in 5 that we’ll win, 1 in 5 that we’ll lose, etc etc. But judges and juries have minds of their own and you never know what new evidence will come to light. There are inevitably other facts, facts the client doesn’t know or feels are irrelevant or not important, that will have a major impact on the case later on.
Still, if the client wants to pay me, and the case and arguments are not frivolous, and the client is not asking me to lie or breach any ethical rules, then I probably will take the case. As long as I don’t make absurd arguments or do anything sanctionable, then there is nothing wrong with losing (as long as the case is not on a contingency).