You need to use your head to solve this problem.

The astronomer conducted an observation of the night sky.

He likes to observe celestial bodies.

It's difficult to guess his feelings.

It's important to believe in yourself.

She uploaded a selfie to Instagram.

She took a selfie and uploaded the photo to social media.

He likes talking about himself and often talks about his experiences and thoughts.

He set out on a journey of soul-searching.

Since that's his own concern, we better not interfere.