What is the mistake that all the marketers fall in ?

I have two view points in this regard

In Product point of view, normally we identify a set of needs of customer and define the features of product to satisfy the customer needs but over a period of time customer needs are bound to change i.e., market shift. when this change happens market shows symptoms and companies will be in a fix whether to react or not, in this dilemma they will stick to their old strategy to handle market and customers. - These are pitfalls where marketers will usually fall.

In competition point of view, Normally when company start its journey they usually have their own USP to project differentiation between them and competitors and they get success and it will become a benchmark, but over a period of time competitors will raise their standards and customers may not find difference between you and competitor. 

In marketing we read about product/service differentiation to be maintained but the meaning of this differentiation will keep on changing over a period of time i.e., marketers need to change the approach consistently.

But most of the marketers will be in denial mode to this change because they think it is against to their earlier thought process. - These are pitfalls where marketers will usually fall.

Not all Marketers are customer focused and sometimes try to force a customer to take up an offer. This may lead to dissatisfied customers and may create a barrier for future opportunities with the customer. This might then lead to profit loss in the long run.

The main mistake is that JUST THINKING & TRYING OF MAKING SALE instead of understanding the needs of consumer in real time and in future.

This irritates the consumer and he departs. If we are able to understand the consumer then he will talk to you in an attractive manner and at that time you may convert that interest into money.