Lazy people stay at home – they say a lion might get them if they go outside.
This is not what I expected the proverb to say. I would have expected it to say “The coward says, ‘There is a lion outside! I shall be slain in the streets!'” But it says, “lazy,” not “coward.” So the controlling emotion here is laziness, not fear. But what does laziness have to do with the danger of a lion in the street? We don’t say, “This person is too lazy to go do their work because there is a lion outside. The presence of a lion does not produce laziness, it produces fear. So what’s the point of the proverb?
The point is that the lazy person creates imaginary circumstances to justify not doing their work, and thus shifts the focus from the vice of their laziness to the danger of lions. No one will approve their staying in the house all day just because he is lazy. But they might sympathize with them and approve their staying home if there is real danger outside. So, to hide their laziness and justify themselves, they deflects attention away from the truth (laziness) to an illusion (lions).