Why is there no smoke when I hit my cart?

I'm curious, why is it that when I take a hit from my vaporizer or e-cigarette, there's no smoke coming out? I've checked the battery, the coil, and the cartridge, and everything seems to be in working order. Could it be that the liquid inside the cartridge has dried up or gone bad? Or could there be some other issue at play here? It's just strange because I'm used to seeing a small amount of vapor when I take a hit, but now there's nothing. Can you help me figure out what might be causing this?