Why do you think Jonas isn't allowed to discuss his training or his dreams with anyone? Why do you think he's allowed to lie?

The strangest aspect of the aftermath of the Ceremony lies in Jonas's peculiar list of instructions, which seems to allow Jonas to break those rules that are most important to the community, such as not being rude, telling his dreams, and in particular not lying. The last rule upsets Jonas, who has been taught to use precise language and to act honestly, so that he will not have opportunities to mislead or prevaricate. This exemption causes Jonas to wonder if all adults are given such rules that allow them to lie, but he can come to no conclusion. This new doubt induced by the rules foreshadows a later revelation of a case in which adults in their training are told to lie.

I personally believe that Jonas isn't allowed to share his experiences or dreams because his friends and family simply cannot understand things the way he does. Sharing would simply result in disbelief and possibly resentment.