If you want to run 5 miles, set a goal of 1.
If you want to workout for an hour, commit to 10 minutes.
Or, according to Twyla Tharp, if you want to commit to the gym every morning, the habit is not the workout, it's hailing the cab for the commute.
Once you cross that 2 mile mark, cheer yourself on. If you feel good, keep going. If not, come back tomorrow and try again. Every day.
Getting started is the hurdle. Once you're in flow, you won't want to stop.
Cheer yourself on for the incremental goals and you'll quickly start to cross the finish line of your lofty ones.