This quote by Abraham Maslow refers to the necessity to approach problems and/or situations using various methods. The analogy of the hammer, the tool, refers to using only one method to solve a problem. The nail is the analogy for that problem. Therefore, to explain the analogy, if we are building a house, a hammer is certainly useful. However, if a hammer is our only tool, we will never get that house built. Therefore, one must implement different tools or strategies to solve a problem; one tool is usually not enough.
For example, consider a company that continually has business losses due to poor communication with clients; this is the nail or the problem. To send bills, this company has always relied on the postal service, the tool or the hammer, and has never done any follow-up with clients concerning their satisfaction. However, this company now decides to offer clients a choice as to how they would like to pay their bills and adds online bill pay, a different tool. As well, they adopt a follow-up questionnaire to check on customer satisfaction, a second tool. Different methods or tools are necessary to solve problems.
Humans have many tools in their tool box. That is, if we cannot solve a problem by one method, we may have to use two or three. For example, in most medical research, rational, analytical thinking is required. However, to find a new cure for a disease, creativity is required along with the scientific process. The different ways of thinking become the differing tools used to find the cure for the problem, the disease.