Certainty not required
Bring all of your doubts and hesitations to the practice with you. Pile them up in front of you, like so many treasures, as you sit down on your cushion to meditate. If you wait for certainty to arrive before you sincerely start practicing meditation (or any contemplative method), you'll never begin.
As soon as you notice some desire in yourself to awaken -- as soon as you receive some teachings that apply to your life -- don't wait another day. Don't let your inner yearning be diminished by the excuse, "I don't yet know enough."
Allow the heart's longing to pull you forward anyway.
Put to good use what you already know.
This is the secret of how to gain momentum on the path.
Uncertainty holds the promise of surrender within it. Even after twenty years of practice there will be doubts and hesitations. It's wonderful news, actually. It means we don't need to have all the answers to achieve profound results on the spiritual path.
We can embrace uncertainty unabashedly. We can take refuge in "I don't know," dive into the great unknown. There is an open quality to this, a hidden potency. It brings freshness and curiosity to our practice. This is what is meant by the expression, "beginner's mind." A beginner is unsure and a little excited to see what might happen if they just go for it. There is a sense of playfulness to the whole dynamic.
This is the spirit of our practice.