Okay, a little silly, yet it is a truth. I write formulas for excel spreadsheets throughout each workday. I have to spell false all day long with h and v lookup formulas. No matter how fast or how slow I go I always spell it fasle. Then excel tells me I am wrong or that ain't a formula. The only thing I can figure is that the 'l' is a right hand function typing and the others are left hand. I don't know. It has only been occurring since the last year. Should I see a neurologist? LOL
For me it is "run" and "ran" - seems simple and innocuous but I have to check which one I meant much later in scripts. It turns out more often than not that I got it wrong the first time. Principle and Principal always put me in trouble with the head of the college where I was a lecturer because I always wrote the wrong title when addressing her in writing - and she would never let it pass.
Stationary and Stationery- Stationary means to be still, whereas stationery is the paper. There are some others but usually I just have to stop and think to realize which one to use. A book called Word Watch by Patricia McLinn is a great tool for words like these.