If you are writing an essay for school and the topic was assigned by the teacher, ask if you can be assigned a new topic. Not having enough information on the topic. Try to do some additional research or talk to others who are knowledgeable on the topic. The more you learn on the topic, the easier it will be for you to write about it. To tired to concentrate.
Writing takes time and concentration.
If you have too many responsibilities that are constantly interfering with your writing, get rid of all of them. Just kidding, of course you can't do that, but seriously, set aside a scheduled time that is only for writing. No interruptions, no phone calls. Your idea is under-developed. Sometimes writers get so excited about an idea that they want to start writing it at once.