There are plenty of design tools available that will ensure that your configuration of components is possible. Such tools can only ensure that the components will fit together. The tool probably has limited capabilities to ensure that you have all of the components that you need (such as cabling), nor can the tool verify that the configuration that you are putting together is an appropriate design for the problem that you are trying to solve. This is the reason why we still need, and most likely will always need, a human being involved in the design process. We need someone to ask the question “Is this the right solution?” and to challenge the design in order to verify that it is indeed the right solution to put in place.
The problem is that anyone who is designing such solutions must make a choice at the beginning of the process that assumes that the design being worked on is appropriate to some extent. Maybe the finer details still need to be worked out, but you must commit to a design early in the process. Research, good questions, and proper analysis will all help you to eliminate wasted efforts on bad designs. Nothing can completely eliminate the possibility that the designer will be blinded by his or her own efforts though once he or she is sufficiently engrossed in the design process.
Nothing except for a second set of unbiased eyes.
Some IT professionals cling to a myth that if they need someone else to verify their designs that they are not doing their jobs. This is ridiculous! Having your work verified by another person of equal or greater ability is the mark of a true professional. It shows that the designer is willing to put results before ego, and that the project is more important than foolish pride. By having your work peer reviewed your design is going to be improved upon or validated as correct. If a mistake is found it will be corrected before it is too late to correct. If no mistake is found you and the person doing the peer review have provided extra value by providing a layer of quality control. There is no downside to an unbiased person with the appropriate skills and level of expertise providing a peer review.
Remember that it is better to have a peer catch something that is wrong during the design phase than it is to explain why the wrong solution was delivered following a failed project. IT professionals crave a good peer review session in order to learn more, improve their designs, and to ensure customer satisfaction. Embrace the process of a peer review and eventually you will find your design skills evolving to a level where fewer and fewer persons will be able to call themselves your peer.