st: Survival data - stset with and without enter() and exit () options

[asb stata <asb.stata@gmail.com>]

I am declaring the data to be survival data using stset command with and
without enter() and exit() options. In one case the total analysis time at
risk is 5869 and in the other case it is 1426901. Can someone explain what
this difference implies? I am missing something fundamental here.

. stset year, id(uid) failure(devstat=1) enter(enyr) exit(mxyr)
               id:  uid
    failure event:  devstat == 1
obs. time interval:  (year[_n-1], year]
 enter on or after:  time enyr
 exit on or before:  time mxyr
------------------------------------------------------------------------------
    4535  total obs.
       0  exclusions
------------------------------------------------------------------------------
    4535  obs. remaining, representing
     716  subjects
     716  failures in single failure-per-subject data
    5869  total analysis time at risk, at risk from t =         0
                            earliest observed entry t =      1960
                                 last observed exit t =      2008

. stset year, id(uid) failure(devstat=1)
               id:  uid
    failure event:  devstat == 1
obs. time interval:  (year[_n-1], year]
 exit on or before:  failure
------------------------------------------------------------------------------
    4535  total obs.
       0  exclusions
------------------------------------------------------------------------------
    4535  obs. remaining, representing
     716  subjects
     716  failures in single failure-per-subject data
 1426901  total analysis time at risk, at risk from t =         0
                            earliest observed entry t =         0
                                 last observed exit t =      2008
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