~といけない (it would be bad if)

Don't go too close to the pond — you might fall in.

She ran away because she didn't want to get caught.

She ran to the station so as not to miss the train.

Thinking I might miss the train, I left home early in the morning.

She's on a diet because she doesn't want to gain weight.

She spoke slowly so her students wouldn't miss what she said.

She handed me the basket and said, since someone might be watching, why not wait until I got home to open it.

I put on an overcoat and went out so I wouldn't catch a cold.

Please close the window so we don't catch a cold.