Some people consider decision of choosing ERP Software is like getting married, are they right or wrong ?

Actually it is right that choosing an ERP software is not that easy specially when the customer has a lots of requirements and specific scenarios to apply.

Moreover, once the client gets a good ERP software (Which is compatible to customer needs) it will be very hard to switch to another one because in this case it will affect negatively specially on the environment itself (Daily work process, END USERS).

Yes, the ERP and the business process must be compatible and the same behavior. The main problem is not at the vendor service provider site. The management  at the customer site needs the benefit of the ERP system without changing their business process to be compatible with the ERP business process.

In this case the divorce between the enterprise and the ERP will be on road.

decision should be taken on right time & decision based on updated realistic data. ERP is the solution you provides real time realistic data if all ERP modules successfully implemented, premature ERP will not support you in this regards.   

To know how your house is going to run, you need to discuss, analyze, find the potential possibilities of your resources, so the argument matches the fact of getting married.