Hard inquiries are made when you apply for a new credit and the lenders check your credit report to make sure you are creditworthy. So, a hard inquiry will imply that you have applied for a new credit. If there are many hard enquiries that means that you have applied for a lot of credit which will look bad to the lenders. And in turn they would be reluctant to lend you the credit you need. If there is an inquiry from a lender, then your credit score will go down by 3-4 points, which will not affect your credit score that much.
Now if there are lenders who make multiple inquiries, then your credit score will be impacted in a major way. Therefore, it is always better to not apply for a lot of credit at once as hard inquiries will bring down your credit score at once. It would also be very hard to juggle a lot of credit at once, and this fact will tip off the lenders and will not get you your credit requirement. Whereas, soft inquiries will not affect your credit score. This is because soft inquiries are made when you check your credit score or when lenders want to know whether you will be eligible for pre-approved offers.