Yes, I do, Gregory.  Get on a different train.  Those side tracks can take you to some very strange places if you let them (such as LossOfEnthusiasmVille, Don'tThinkICanDoItopolis, and, even, WhatTheHellWasIWritingAnwaysburg).  And definitely slow down your journey.  Or even stop it, all together.  That may sound like a flippant answer, but, deep within its apparently laissez-faire sentiment lies buried a profound and arcane truth (although, what that truth is completely escapes me at the moment.  Escapes me like a runaway train.  That's it!  That's the truth!  Don't get on a runaway train!  No, that's not it.  Maybe by the time I finish this article, the profound, arcane truth will come to me.)

My solution for not getting sidetracked (besides not getting on a runaway train) is to, basically, "keep the fires burning."  Keep the stoking the fire (and I'm not talking about the one on a runaway train that is sidetracked.  Did you ever notice that somebody can overuse a metaphor to the point where you want to do them bodily harm?  Or push them off a cliff?  Or off a runaway, sidetracking train?)  The fire I'm referring to is that of your desire.  It's imperative that you continue to fan the flames of your desire, to keep remembering what you want (in this case) in terms of your screenwriting.  Keep asking yourself this most critical question:

what do you want?

I mean "What do you really want?" when it comes to your desires concerning your screenwriting.  What I'm getting at here is that what "sidetracked" you is just another desire!  Maybe some ice cream had your name on it.  Or you got a "call of the wild" from the Great American Novel.  Or maybe you got one from the opposite sex (very wild, you naughty non-writing screenwriter, you!) that you just couldn't refuse (and you've returned now after a year and half, ready and willing to get back to that script you had just started.  What was the title, again?  Oh, yes:  "Obsessive Obsession":  A horror based on a true story.)  It's your desire that will keep you on the path towards your goal.  But you must know and remember and remind yourself repeatedly about what exactly that goal is.  

I find that I get bogged down frequently if my NEXT goal is not clear and achievable.  Sometimes, even the goal of "finishing the screenplay" can seem daunting, and I have found that breaking that goal into smaller goals, "goalettes," (I think that was the name of group of dancing -- and skating -- girls for the NHL)  is the only thing that works -- especially if I'm feeling overwhelmed by the screenwriting task at hand.

Here's a typical example of the "incrementalization process." (The IP, as the Incrementalization Processors call it):

THE OVERALL GOAL:  To Write and Finish The Screenplay

The goals that lead to the overall goal (overall):

1.  Get up earlier than 4:00 p.m. (if you don't, take heart; go back to bed and wake up at 4:00 p.m. the next day, feeling refreshed and-- No, that won't work.  Forget that one.)

2.  Decide what kind of screenplay you're going to write.  Be perfectly clear about that decision and what you've decided to write.

3.  Decide that one again (and as many times as necessary until you're tired of driving yourself crazy about trying to finally decide and finally make a decision).

4.  Even though you're filled with intoxicating enthusiasm, before you set to writing (which I think pioneers from the Wild West did when they started their screenplays -- which usually were of the Western genre), decide what your list of goals will look and feel like as you tread the path to your final goal, that of finishing your screenplay:

Maybe something like this:

Write the following and in the following designated order:

1).  log-line

2)  treatment

3)  outline

4)  grocery list

5) story beats

5)  scenes of major turning points

6)  your bills

7) the final scene 

8) your will

9) and testament

10) the opening scene

11) other scenes that seem to call to you

12) your congressman

13) all the boring scenes that you don't want to write, but you know you have to

14) all the exciting scenes that you want to write, but now don't seem so exciting

15) suicide note -- no, don't!  At least, not until you've finished your screenplay

16) scenes that you forgot you would need to write and wish you didn't have to

*Now, at this point, you could be experiencing the dreaded 80/20 syndrome, which we all know goes as follows:  

"takes 80 pounds of coffee, sugar, and a myriad of mood enhancers to write 20 pages of a screenplay."  

But don't let that get you down.  You can break through this barrier.  Like a track star.  A jittery, overweight, and who-knows-what-else track star.  Pat yourself on the back; you made it.  

now finish that script

Good work.

Now you can start your next list:

Producers Who Don't Know Who I Am Or Even Care That I Even Exist And Whom I Want To Send My Finished Screenplay To, Even though they probably won't read it or only a few pages after all my work that I did by writing down my goals and keeping the fires of my desires fanned (or will give it to some underpaid reader who is looking for a way to not like it and only desires to go home early):

DcH