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!'
Primum non nocere: "first, do no harm."