Lessen and listen are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It suggests what word you may want to save time, but quite often, its suggestions are more funny than useful.
Lessen is a verb. It means to decrease or make something easier.
Listen is a verb. It means to pay attention to, hear, and respond to another person who is speaking, or pay similar attention to one’s surroundings.
The following story uses both words correctly:
Loesser, a rabbi, was a pillar of his local community. He had a reputation as a compassionate man, an exceptional listener, and someone he did all he could to lessen the suffering and burdens of the poor.