Logic vs Karmic principles Imagine this hypothetical situation (which is meant to simplify the scenario in this question):

There haven't been any past lives -- this is your first life, and therefore there is no past karma, but only the karma[s] you make in this life.
(So, in this imagined version of events, we can use the knowledge at hand without complications clouding our judgement.)

The universe is in it's first cycle, and birth has happened for the first time.
(This further eliminates any doubts of the unknown, and allows us to work with our hypothesis.)


Now imagine the following two events/actions:

Imagine walking out into the streets and seeing a hungry puppy and feeding it your lunch out of kindness/empathy and happily walking into your workplace in the bliss of doing something nice with your lunch, instead of eating it like always.

In the lunch time an old enemy of yours taunt you and this leads to a fight which ends with him arm being broken by you (intentional).


The question is: can you explain why both event 1 and event 2 would effect the next life?
As there is no Soul/Person/being in our teaching, what we have is a self responding, self generating and a replicating consciousness. If there was a soul or a being, we can justify this by saying &quot;I am being rewarded for my good and being punished for my faults&quot;.
But we are without such permanent identities: what we have is a consciousness that gives birth to thoughts and disappears ... one thought would arise from another, but all thoughts have their own identity, apart from its parent thought (this is much like we and our parents).
On what basis can we attach the karmas of different actions together, when there is only emptiness (Anatta) between 2 different actions?
The answer for this comes in the Acela Sutta (although this quote comes from here). Of course, the question was phrased differently by Kassapa, but the essence of the question is the same.


  Again, when the Buddha was asked by the naked ascetic Kassapa whether
  suffering was of one's own making or of another's or both or neither,
  the Buddha replied "Do not put it like that." When asked whether there
  was no suffering or whether the Buddha neither knew nor saw it, the
  Buddha replied that there was, and that he both knew and saw it. He
  then said "Kassapa, if one asserts that 'He who makes (it) feels (it):
  being one existent from the beginning, his suffering is of his own
  making,' then one arrives at eternalism. But if one asserts that one
  makes (it), another feels (it); being one existent crushed out by
  feeling, his suffering is of another's making,' then one arrives at
  annihilationism. Instead of resorting to either extreme a Tathaagata
  teaches the Dhamma by the middle way (by dependent origination)".


The second useful sutta is the Acintita Sutta which states that the precise working out of karma cannot be conjectured:


  "The [precise working out of the] results of kamma is an
  unconjecturable that is not to be conjectured about, that would bring
  madness &amp; vexation to anyone who conjectured about it.


The third useful quote below comes from the Sivaka Sutta, teaching that not everything we experience in life is due to karma. Some times it's due to the weather or indigestion etc.


  As he was sitting there, he said to the Blessed One, "Master Gotama,
  there are some brahmans &amp; contemplatives who are of this doctrine,
  this view: Whatever an individual feels — pleasure, pain,
  neither-pleasure-nor-pain — is entirely caused by what was done
  before. Now what does Master Gotama say to that?"
  
  [The Buddha:] "There are cases where some feelings arise based on
  bile. You yourself should know how some feelings arise based on
  bile. Even the world is agreed on how some feelings arise based on
  bile. So any brahmans &amp; contemplatives who are of the doctrine &amp; view
  that whatever an individual feels — pleasure, pain,
  neither-pleasure-nor-pain — is entirely caused by what was done before
  — slip past what they themselves know, slip past what is agreed on by
  the world. Therefore I say that those brahmans &amp; contemplatives are
  wrong."
  
  "There are cases where some feelings arise based on phlegm... based on
  internal winds... based on a combination of bodily humors... from the
  change of the seasons... from uneven care of the body... from harsh
  treatment... from the result of kamma. You yourself should know how
  some feelings arise from the result of kamma. Even the world is agreed
  on how some feelings arise from the result of kamma. So any brahmans &amp;
  contemplatives who are of the doctrine &amp; view that whatever an
  individual feels — pleasure, pain, neither pleasure-nor-pain — is
  entirely caused by what was done before — slip past what they
  themselves know, slip past what is agreed on by the world. Therefore I
  say that those brahmans &amp; contemplatives are wrong."