Because the sci-fi comedy about an Alien Life Form (or ALF for short) that aired on NBC didn't have a computerized main character (it was actually a puppet) all kinds of bizarre arrangements had to be made to shoot the series.

Which meant avoiding a huge number of pitfalls. 

"The actors couldn’t simply walk anywhere they wanted because the floor contained openings for the puppeteers. Whenever ALF had to move, the production could lose considerable time getting the puppet into position. Anne Schedeen, who played Kate Tanner, even recalled falling through one of the openings during filming."

Surprising for a character whose catch-phrase was "No Problem!"

40 Years Ago, An Iconic Sci-Fi Sitcom Premiered & Was Hell for the Cast (& It Starred a Puppet)