One of the most common word confusions I see, even in writers who aren't easily confused, is between "effect" and "affect". It's very understandable - both can be a verb, and both can be a noun - and sorting it out is a bite-sized job, so here goes, with a little help from the Cambridge and Merriam-Webster dictionaries.*
You most often meet effect as a noun. It has many uses, but the one we mostly meet is "the result of a particular influence":
- The radiation leak has had a disastrous effect on the environment.
- It's too early to predict the effect of the report.
- Watch the effect of his announcement on the audience.
- She had to wait for the anaesthetic to take effect before she could stitch up the cut.
- I think he loses his temper in meetings largely for effect.
- So in effect the government have lowered taxes for the rich and raised them for the poor.
- Winter opening times and regulations are now in effect.
You most often meet affect as a verb and it usually means "to have an effect" or "to cause a change" on something or someone:
- His illness affects almost every aspect of his life.
- Both buildings were badly affected by the fire.
- Her narcissistic rages are affecting the children too.
- You couldn't fail to be affected by this novel.
- These new results do not affect the conclusions of this report.
- The timing of this recipe may be affected by the ambient temperature in your kitchen.
Affect as a verb can also mean to deliberately put something on:
- He says he's leaving and she affects indifference to the news.
- The band affect a careless, informal style of dress.
- She's recently affected film-star type hats.
And from that usage we get the adjective affected, meaning artificial and not sincere:
- His apartment was incredibly affected, all pink silk and fake antiques.
- After those terrible reviews her writing becomes more affected, full of dramatic pauses and crude words.
But both words can have other forms, which has the effect of affecting many writers' confidence in using them. (see what I did there?)
Effect as a verb is closely related to the noun, meaning "to cause something to happen", "to achieve a certain result":
- We must effect a complete return to more sustainable practices.
- By abandoning my lunch, I effect a discreet departure (compare "I affect a discreet departure", which would mean to change the style of exit, not to achieve it successfully.)
- Effecting change is possible, but it's very slow and difficult.
- Only a police officer can effect an arrest for this type of offence.
- Watch! A great change is being effected!
Affect as a noun is a rather different beast, which goes back to Chaucer but nowadays only shows up in psychology and psychiarity, derived from the German Affekt. Here, it means a feeling or subjective experience, an emotion or mood: either the outward signs, or the feeling itself.
- The patient showed perfectly normal reactions and affects.
- A flat affect is often the most obvious symptom of depression.
- Joy, love, contentment and bliss all come under the umbrella of positive affect.
- An affective account of this individual's life would emphasise the dominance of mood-swings in determining their activities. (OK, that's an adjective, but you get the point.)
So I do see why writers find it confusing, but it's not actually that complicated. Good luck!