Reading those of you who scorn belief... I wonder... before the Buddha was the Buddha, before he knew and saw Nibbana... we at least can develop confidence in his word... what did he have to go on?
"Seeing the danger in sensual pleasures — and renunciation as rest — I go to strive. That's where my heart delights." — Snp III.1
How did he know renunciation would be rest and not frustrated deprivation? Certainly the five ascetics were well practiced at renunciation and just as certainly they were not at rest.
"In this way did Alara Kalama, my teacher, place me, his pupil, on the same level with himself and pay me great honor. But the thought occurred to me, 'This Dhamma leads not to disenchantment, to dispassion, to cessation, to stilling, to direct knowledge, to Awakening, nor to Unbinding (nibbana)." — MN 36
How could he be sure there was such a Dhamma which would lead to disenchantment, to dispassion, to cessation, to stilling, to direct knowledge, to Awakening, to Nibbana? He had already sought out the wisest teachers he could find. How could he know if there was anything more to learn?
"I thought: "Whatever priests or contemplatives in the past, future, or present are feeling painful, racking, piercing feelings due to their striving, this is the utmost. None is greater than this. But with this racking practice of austerities I haven't attained any superior human state, any distinction in knowledge or vision worthy of the noble ones. Could there be another path to Awakening?'" — MN 36
Maybe there was, maybe there wasn't. He couldn't have known, right?
"I thought: 'Could [jhana] be the path to Awakening?' Then, following on that memory, came the realization: 'That is the path to Awakening.'" — MN 36
He realized... what does that mean exactly? He knew? He believed? He hoped? He hadn't seen for himself yet. He didn't even have someone else's word to go on since no one else had seen either.
"My heart, thus knowing, thus seeing, was released from the fermentation of sensuality, released from the fermentation of becoming, released from the fermentation of ignorance. With release, there was the knowledge, 'Released.' I discerned that 'Birth is ended, the holy life fulfilled, the task done. There is nothing further for this world.'" — MN 36
Now there was knowledge. Now there was no more room for belief. But I wonder... what about up to that point?
Be heedful and you will accomplish your goal.