Each bird has its own personality. Cockatiels are socialable creatures, if you only have one , he or she will probably want to be around you a lot. Giving him or her a friend will allow them to entertain each other more often.
I got lucky with my cockatiel, she is fairly independent for a tiel. She doesn't mind preening on her playstand, playing there , foraging for food really keeps her occupied as well. However, if she sees me close by with an iPad, which is her favourite toy , she will fly on my iPad and pretend she is browsing the internet or chew on the corners. She also flies to my head if I leave the room 80 percent of the time. She rarely does this for my boyfriend. However, she flies to him sometimes to see what he's up to. She also does the same with me. So when she is out of the cage 50 percent of the time she's independent, 50 percent she's doing her own thing. I think it is because she is a very playful bird , that she is fairly independent.
I've read some tiels that cry to be attached to their owners at all times, some wild ones that are scared of people.. they come in all personalities and their past does play some part in how they act. Birds that are introduced to toys at a young age tend to be more playful.