It increases development costs. If engineers do not choose the simplest solution to address a problem, the costs in time and money increase, preventing us from iterating faster. 

It also increases your maintenance costs. Simple code is much easier to program, test, and modify. When you complicate it, the complexity can grow exponentially, impacting our iteration speed.

The best way to prevent over-engineering is to turn your engineers into true product engineers.

• Involve them in the day-to-day business, explaining the why after each initiative, and linking it with the metrics that matter for the organization and its vision. 
• Bring them closer to the users, inviting them to interviews and discovery sessions with them. You want your team to empathize intimately with your user’s problems, so they can quickly discard any engineering effort that won’t solve them as efficiently as possible.

• YAGNI(“You are not going to need it”) tries to prevent you from adding anything that is not strictly necessary to solve the problem you have in front of you because the reality is that most likely, “you won’t need it”.
• KISS (“Keep it simple stupid”), refers to the fact that simple systems are easier to repair, evolve and maintain. Therefore, simplicity should be one of the goals of any design.
• Worse is better: There comes the point when having fewer options is preferable to having more; Simplify the use of our product, making it attractive to a broader segment of the market.