Specific: This assumes that the picture you currently have of what you want is the thing you actually want. Do you want faster horse, a Model T, or swift reliable transportation of a form you've not yet imagined.
Measurable: If you only value that which has a number, you'll lose sight of what truly matters in life because of the Streetlight Effect[1]. Consider the ridiculousness of the question "What NPS score would your children give you?"
Attainable: There is a limit to the degree to which you can "be sure" of anything, especially without 2020 vision.
Relevant: This requires really knowing what your values are so that you can practice the subtle art of not giving a fuck[2] about other things. Determining those can be hard emotionally-painful work, but in any context it is a good problem you want to have solved.
Time Bound: Sometimes deadlines spur action, sometimes they paralyse or cause you to lose sleep. Sometimes, they are so far off in the future that you don't think about them until it is too late because you thought you could do them. If you're looking at a timescale longer than 6 weeks, consider instead that you might want a CGP-Grey style Theme: https://www.youtube.com/watch?v=NVGuFdX5guE
[1] https://en.wikipedia.org/wiki/Streetlight_effect
[2] https://www.audible.co.uk/pd/The-Subtle-Art-of-Not-Giving-a-... Highly recommend this to anyone who spends lots of time thinking about personal goal-setting.