In my view, this statement is completely true. It is extremely important to have a marketing plan. If you do not have one, it seems unlikely that your marketing efforts will succeed as well as they should.
In order to do a good job of marketing, it is important to really think about what you are going to do. You have to think about the message that you are trying to send out about your business. You have to determine what it is that makes your product special and you have to think about how to convey that idea to your potential customers. You also have to think about who those customers are. If you do not know who your target market is, you will waste your marketing budget. You will be more likely to spend your money trying to reach people who are not likely to ever buy from you. At the same time, you will be failing to reach people who would actually have been in your product. This will set your business up to fail.
If you do not plan your marketing, you are likely to fail. You will waste your marketing budget while failing to reach the people who are most likely to buy from you. This will harm your business. At the very least, you will have failed to grow your business as much as you could have with better planning.