I've gone 6-8 weeks without missing a day. People have said "don't beat yourself up if you miss one day here or there" and I've gone up to 6 months without missing 2 days in a row. It has never become automatic.
The only thing that works for me, at all, is putting things directly in my way so they're practically unavoidable, and physically removing distractions in advance. Modifying my environment to make the things I want to do extremely easy to do, and the things I don't want to impossible or difficult, is the only thing that works.
