Your voting strength is limited because there's only so much daily mined crypto to give out each day. The more Steem Power a person has in their account, the more of the daily amount they can give out. Your voting strength recovers about 20% a day, so most people suggest you keep your voting power above 80% day to day. People should try to vote only on things they want to support since their voting power is limited. There's more about this in the information I'll share in my main reply...