I usually chuckle and say, "Well, you can't get to the runner's high until you get over the runner's hump." When you're new to running, you can hardly imagine running 2 miles, much less 6, 8, 10, or more. For some they're content with running 2-4. There's nothing wrong with running 2-4 miles, but more than likely if you never push past that 2-4 miles, your run is always going to feel somewhat uncomfortable.
It takes your body 4-6 weeks to actually acclimate to a specific distance. That doesn't mean that you should run only 2-4 miles for 4-6 weeks. But, what it does mean is that when you run that 2-4 miles and keep pushing the mileage up a small percentage each week, in 4-6 weeks (when you're longest run may be 6-7 miles) you're body will have acclimated to the 2-4 miles.
Often new runners never give themselves a long enough period of time for their body's to adjust to the mileage. They also need to understand that those first two or so miles are usually a little uncomfortable for even the seasoned runner. It takes those first few miles for your body to adjust to your increasing heart rate as well as just the fact that your muscles need some time to warm up. In fact unless you're running a race, that first mile or so, should be thought of as a warm up easing into the regular groove of your run. I've been running for 25 years and I still don't look forward to the first 2 miles, but I know that once I'm past that point, it's going to feel good. I've usually got my "groove on" by mile 3. (Okay, I just embarrassed, my 14-year-old daughter.) But, it's true. By mile 3, everything is in sync.
New runners may also be ramping up the mileage too soon. A good rule of thumb is to increase your weekly mileage by 10% and most of the 10% can be added to your weekly long run. Now at first, when you're running only a mile or 2, you might be able to get away with increasing the mileage by 15% or so, but once you're up to 5- to 6-milers, stick to the 10% rule. If you push it too soon, you're not giving your body time to acclimate. (Remember that it takes 4-6 weeks to adjust to a given mileage). Too much too soon can cause overtraining (even in a new runner) and then you're going to feel sore and worn out each time you run.
So, take your time, slowly build up your mileage, and get yourself past that 4-mile hump. Be realistic though. Once you get past that 4-mile mark, the sky's not going to open up and the angels aren't going to sing the Hallelujah Chorus, but I'm willing to bet you'll feel different, and it will be a good different.
That runner's high you've heard tell about, usually occurs when runners work up to longer runs say 8 miles or more. These runs, give you time to warm up, get in your groove, set your pace and then just run. Once you get to this point, you may just hear that Hallelujah Chorus. For me, it's like an outer body experience. I'm able to think, problem solve, enjoy my surroundings, and the running almost seems second nature. It doesn't happen on every long run and on hard runs when you're really pushing it, you're probably not going to feel it, but when you do, it's a feeling you'll want to experience again and again.