For obvious reasons, it is extremely important to have a suitable shelter to sleep, store items, keep beasts out, etc.
But even in your home, you aren't 100% safe from the beasts that hunt you at night.
As you can see in the pictures below [which were taken by Stanimus on the SC Wiki], the lion is poking his head through the door and leaf blocks.
Now, the shelter is not the problem. Stanimus has made himself a nice beginning shelter made from dirt and leaves, in what appears to be the side of a mountain. The lion - and other predators - can poke their head into your home no matter what material you use!! [This is especially apparent in corners, as you can see in the second pic above, and the spot where two different blocks meet.]
I have experienced this myself. Whenever I slept by my door, a tiger, werewolf, etc. would always injure me in my sleep!!
So it is a good idea to make your house out of 1 material so that the only spot predators can poke through into your home is by your door. Also, just to be safe, sleep in the middle of your floor ;)