Thankfulness for Capability (or Means) is also Necessary

If we are receiving sustenance or help from some means, we must be thankful for these too. However we should not consider these means or intermediaries to be independent of Allah. We must accept them only as the agents through whom Allah is causing His Mercy to reach us. These agents only act as a medium of passing the bounties of Allah and hence they must also be acknowledged; as ordered by the Masoom (a.s.). 

"One who does not thank his apparent giver (the agent or the means), it is as if he has not thanked his real giver (Allah)."
(Behaarul Anwaar)

"The most thankful amongst you towards Allah is the one who is most thankful to the people (who have helped you)."
(Safinatul Behaar)

There is no doubt that if one considers his helper to be the original doer of good (independent from Allah), he has surely committed shirk.