You were hungry. The only thing you found was a cup of warm milk. Nothing quite as satisfying as that, you thought to yourself. An hour later your tummy was rumbling and feeling bloated. The discomfort somehow passed after nagging you for a few hours. You moved on with your day as usual.
Just like you, most people go through their lives without even knowing that they are Lactose intolerant. Especially in cases where the symptoms are not as pronounced but bothersome nevertheless.
According to wikipedia, data suggests that 65% to even 90% of the population in some communities have a reduced ability to digest lactose. Some studies have shown that 3 out of 4 Indians also have a lower milk tolerance.