I have had doubts in my practice, have sometimes taken to heart a bit the subtle criticism I once heard implying that in the Theravada we are practicing 'to liberate ourselves' and are thus not as pure as those who pursue the Bodhisattva ideal. I have, after MUCH reflection, decided that since the Pali Canon is the closest historically accurate record of what Buddha actually taught, and since I feel I can trust this man (he seems very consistent, he claims NOT to have divided the teaching (into 'common' and 'secret'), if I trust him then I can take HIS words to heart. And I don't hear him say 'Do what I did, practise paramitas for many kalpas (and I bow deeply to any being who actually does this) and become Sammasambuddhas yourselves'. He rather seems to say 'You have attained the human form of life, which is very rare; during a time when the Buddha-Dhamma is extant (also rare); with an intellect capable of grasping the necessity of practising (even more rare). Do not miss this opportunity!'
When this is, that is.
From the arising of this comes the arising of that.
When this isn't, that isn't.
From the cessation of this comes the cessation of that.