The case against suicide
And whence is one supposed to get the optimism to believe this argument or see it as relevant?
Presumably every person has a breaking point, some just reach theirs temporally sooner than others. Once a person has reached that point, based on what can they still see their particular predicament not only as temporary, but, more importantly, that many better things are yet to happen for them and that their life will be nice and easy from that point on until the end
Several things.
First, the source of the "optimism" is the Actual Data that proves that among those in your exact situation (contemplating suicide), the vast majority (70 - 93%) will change their mind and decide that life is, in fact worth living after all. Though your implication is correct that many can not or will not understand or accept that data. But that is an error.
Additionally, we all continuously make a calculation that weighs the positives and negatives associated with continued existence. And you are correct some reach the point whereby the calculation tips to favor suicide. Say someone comes to that point at age 24. Statistically such a change is commonly brought about by a sudden, unanticipated negative (divorce, death of a loved one, financial or professional loss). That is: an acute event, as opposed to the effect of accumulated chronic issues. Think about it, if everything was going great for me then in a week my dad dies, my wife sleeps with my best friend and divorces me and my business is sued and goes under, my calculation will switch from "worth living" perhaps to "not worth living". However, fast forward 2 years, the death of a parent is something essentially everyone comes to grips with, as is divorce and bankruptcy. You'd be in a totally different mindset than the previous time point. OTOH, if I was born into abject poverty, with no family support, no economic resources and clinical depression, and I have reached the age of 24, by definition my calculation at age 23 was "worth living", so maybe at 24 it has tipped to "not worth living". Well considering what I have (successfully) dealt with all my life probably what has changed is my clinical depression (since everything else is rock bottom). Clinical depression is notorious for it's roller-coaster trajectory of ups and downs, that is how you're feeling is likely temporary.
Lastly your goal of life being "nice and easy" is a false one. Loads of people with not nice and not easy lives believe their life is worth living, which is the decider in this context.