The problem is not reflection
Most people who say they cannot keep a journal can reflect perfectly well. What they cannot do is produce a paragraph on demand at the end of a long day.
So remove the paragraph. What follows is a method that keeps the looking back and drops the writing.
One fixed moment
Pick a moment you already have every evening. Brushing your teeth, plugging in the phone, turning off the kitchen light.
Attach the reflection to that moment and nothing else. A habit tied to a time of day survives, a habit tied to motivation does not.
Five questions, not one
One question is too few, because a day has more than one side. Twenty is too many, because you will not do twenty tomorrow.
Five is enough to cover the day: how heavy or light it was, how much energy you had, how connected you felt, how present you were, whether it had any sense of meaning.
Keep the wording identical from night to night. A question that is phrased differently each time gives answers you cannot line up.
A scale, not a sentence
Answer each question on a scale from one to ten, against your own usual. Not against a good life in general, against your own ordinary Tuesday.
A scale takes two seconds and asks nothing of your vocabulary. It also makes tonight comparable to last Thursday, which a sentence never is.
Read the pattern, not the day
Do not interpret a single evening. A heavy day is a data point, not a verdict, and it only means something next to the days around it.
After two or three weeks, look at the whole row. That is where the information is, and it is almost never where you expected.
This works on paper
A notebook with a grid does the job. One row per evening, five columns, a number in each cell, and a glance across the rows on Sunday.
The only thing paper cannot do is ask you a different question tomorrow based on what you answered tonight.
Keep the notebook where the moment happens, by the toothbrush or on the charger. If it lives in a drawer the habit will too.
If the phone should do it
Insenia is this method as an app: five questions each evening, answered with a slider or a tap, never typed, in about a minute. The questions change each night and follow up on what you said the day before.
Each evening becomes one colour, and the pattern is read for you after about two weeks. You can tryfive real questions tonighton the web first, with nothing to sign up for.