That's a good question because that's what I actually used to believe - until I grew up! I thought dreaming was only what kids did when they say things like "I want to be a fireman when I grow up". But I found that I was very wrong. Now doesn't 'goals' sound much more professional and mature than 'dreams'. Yes, you might say having goals is not childish, but really goals are just dreams with a deadline. Say for example your dream may be to own your home outright. This dream will then be broken down into smaller goals with timeframes attached in order to achieve that dream. Dreaming is considered by many to be immature because it's emotional, but worrying is considered mature. However dreaming is simply planning for what could or might go right in your life. Worry is no more mature than dreaming because worry is emotionally planning for something that might go wrong in your life. So really worry is no more mature than dreaming because worry is not based on what has happened. Both are emotional, neither one have happened and there is a need for both.
Dreaming is a form of mind framing. Frames are mental structures that shape the way we see the world. Our minds rely on frames not facts, so much so that the human experience will reject facts if they dont meet the concept we have (the frame). So in other words we reject factual information that is not connected emotionally. So if you don't have a dream that is visual and clear enough in your mind it wont move you to make the decisions needed to achieve it. You need to build your dreams to move you - only then will you be motivated to make changes. Make sure you never let anybody kill your dreams. So why not start dreaming now to get you motivated!