That old retainer case in a drawer is proof you once stuck with something for two straight years. You can do it again.

You already have evidence of your own stubbornness, and it is usually in something unglamorous you never thought of as discipline. Two years of a small daily annoyance uses the same muscle any long project needs. People who think they cannot stick with anything have often just never counted what they already stuck with.

Write down three things you have kept up for more than a year, including the boring ones. Keep that list for the next time you decide you are not a consistent person.