I keep the habit for eleven days then miss two and never restart Restarting

Nothing breaks at day eleven. What breaks is that the streak was the motivation, and once it's gone there's nothing underneath it.

Streak-driven habits have a built-in failure mode: all the value of continuing is stored in the unbroken chain, so a two day gap doesn't reduce your motivation by two days' worth, it deletes all of it. That's why it's a cliff rather than a fade.

What's worked for me and for most people I know who got past this:

• Plan the miss in advance. Decide now what happens when you miss two days, because you will. "I run the next scheduled day at half distance, no making up" is a rule you can follow while feeling bad.
• Count weeks, not days. Three runs a week, and a bad week is one out of three rather than a broken chain. Fifteen good weeks out of twenty is a real result and there's no equivalent partial credit in a streak.
• Make the restart tiny and pre-defined. Not "get back on the plan" but "shoes on, run to the end of the road". The restart has to be easier than the habit, not equal to it.

The fourth attempt this year isn't failure, incidentally. It's the fourth time you've started, which is more than most people manage.

Running-specific: the day nine to eleven cliff might partly be physical. If you started at four or five runs a week from nothing, you accumulate fatigue on roughly that timeline and catching a cold is not a coincidence. Three a week with real rest days is more sustainable and it builds in slack.

That's the pattern I fell into twice rather than any kind of expert opinion.

Attach it to something that already survives disruption. I stopped trying to run in the morning and started running after the school drop-off, which happens whether or not I'm motivated. Work trips still break it but the recovery is automatic because the anchor comes back.

Also worth asking whether you want to run or want to be someone who runs. Four attempts with no missing-it feeling when it stops is worth sitting with. I spent three years trying to be a runner before admitting I like cycling, and I don't have this problem any more.