You've probably heard that hiring managers spend something like 10-30 seconds looking over a resume. Most people hear this, but don't believe it. After all, they've put so much work into their resume, so certainly they deserve to have it read thoroughly.
Regardless of whether it's fair, it's true. And the more crowded the job market, the more applications a hiring manager has to read through, meaning the less time they can give any one application.
So you can't make a hiring manager spend more time on your application, at least for the first pass through. If they like what they see after skimming it, they may read it more closely either before or after inviting you for an interview. But until you give them a reason to, they're not going to treat your application as any different from the hundreds of others.
This is important to keep in mind when deciding what information to put into your application and what to leave out. You already know that your resume isn't going to contain everything you've ever done. So you have to decide what's important enough to stay, and in doing so, you want to be mindful of the fact that it's going to be skimmed.
You don't want the hiring manager to get one message if they happen to read these five lines of your resume or cover letter while skimming it, and a completely different message if they read these other five lines.
Your resume and your cover letter together tell a story about who you are, what you've done, and why you're applying to this job now. That story can be a complex, rambling story including lots of filler details. Or it can be a concise, compelling, focused story with a single key message you want to communicate.
Given that you've got less than a minute to make an impression, which type of story do you think it should be?