You could be smokimg shit weed or you could not be inhaling it.

I remeber my very first time smoking I didn't get high, but I also remeber not inhaling ciggs. right at the time and perhaps I didn't inhale that joint at all. I'm not really sure, but I do remeber when I finally taught myself to inhale, and it was tobacco. I got so bloody sick! It was awful.

The second time I smoked though was out of my dads old bong and I got blitzed.

So yeah, just make sure you are inhaling the smoke. Better weed helps too. If you're smoking shitty weed then you won't get anywhere.