Although we have a separate section on resume customization, we want to point out here is that cover letter is an important part of a resume, in fact, it compliments your resume and makes it whole. We always learn better from examples so here we are describing a situation and its potential corresponding letter.
Consider this situation:
One candidate went to college for a certain degree (in a booming field at that time) and continued his/her higher education in the same field. By the time of completion, however, the job scenario has changed and the field that was booming before is now not that intriguing anymore, moreover, there are more people and fewer jobs.
Their only options at this point are:
Option 1: Get a lower-paying job in the same field. While this could be rewarding in some sense, it is more likely that they get frustrated with the time and lose interest in their job.
Option 2: Another option is to look for some new degrees and certification in some other field: this is interesting and challenging at the same time since you will have to explain to the companies about why you want to switch fields and join a new one.
This is one of the many other situations where a carefully customized cover letter can be used to explain your resume and get the perfect job in a new field.
Sample of the cover letter:
Dear Hiring Manager,
I John Doe would like to apply for xxxxx position in your esteemed XYZ company. I wanted to take this opportunity to show my deep interest in this position. While from my attached resume you can find that most of my education has been in yyyy field. During my education, I realized that I could greatly enhance some of the processes and by applying zzzzz (example subject) skills. In order to enhance my capability, I later enrolled in this zzzzz (example subject) certification course and was able to successfully apply the techniques I learned to enhance my work. I want to show a similar kind of commitment to your esteemed company and bring my skills to excel in this position.
Thank you for your time and consideration.