There's no such thing as the meaning to life. There are only meanings, and the most meaningful life has 1) meanings that provide the deepest sense of satisfaction and self-transcendence, and/or 2) continual meanings ideally like in stepwise fashion: after one comes another, then another, then another.
What does it mean to say that the meaning of life is to "be rational"? It means that being rational is, by itself and solely by itself, what should motivate us each waking moment of every day -- hence the meaning to life. What does that look like? Not life. Living in abstraction trying to patch up the sky castle of your reasoning is something that's actually antithetical to life, because life means to some degree doing things like, I don't know, walking, talking, looking at sunsets, playing an instrument (or not), and other things.
Precisely because any meaning to life is singular, it can't be adequate to provide a fulfilling and self-transcending life, which is what a meaningful life looks like. Saying there is a meaning to life means your life is very dull, monotonous, repetitive, and that's no life worth living. Therefore, reductio ad absurdum, life is multimeaning, polymeaning, strings of meanings, not singular meaning.
Dig it?