Are you tripping a lot in-game?You're either:
having "bad luck"
Luck is random per day - if you visit Katrina, the Fortune Teller, 20 times, she'll open up a shop on the strip and you can ask her. Or, if you buy Redd's Fireworks Cookies 4 weeks in August, there is an item called the "Lovely Phone" you can win that you place in your home. You can then call it every day to hear your fortune and lucky item.
are wearing the King Tut mask
The mask is an item that is cursed.
don't have rain boots on when it's raining
Seriously, buy a pair and either use 'em all the time or save 'em.
OR are inappropriately dressed for the season
If you, say, have long sleeves in the summer, etc - you're wrongly dressed. You can see this if when you come out of your home your character does a little animation, like 'OMG I'm hot' (wiping sweat from brow).
Brewster won't let you work?work time is only 11 am to 11 pm every day
is it a festival/holiday?
He won't let you work.
is there anyone in town
(Sabrina, Redd, Joan, etc)? He won't let you work.