Speech is a very powerful tool. If we hit someone, it will hurt for a short time and then go away. But if we verbally attack someone, those words can stay with them for many years. On the other hand, well thought out words can stop conflict, make friends and heal rifts. This is the power of speech and this is why Buddha included Right Speech in the Eightfold Path.
Right Speech can be divided into four parts, namely refrain from lying, refrain from divisive speech, refrain from harsh words and refrain from gossiping.
When we tell lies it is obviously going to hurt and mislead others, but it will also harm ourselves. Nobody likes a liar, and once you get the reputation, it is difficult to lose it. Whenever you tell people things they will not believe you, even if it is true. They will try to avoid you and you will find it difficult to make friends. This will of course make you angry and frustrated but you will only have yourself to blame.