The 36-year-old insists that the loss to Serse Cosmi's side will not derail their season, and maintains that he has confidence in his team
Stramaccioni oversaw the Nerazzurri's second home defeat of the season, with second-half goals from Simone Vergassola and Francesco Valiani giving Serse Cosmi's side a convincing victory.
Nevertheless, the 36-year-old expressed his "great confidence" in his playing staff, despite now going on a run of five home games without victory so far in 2012-13.
"The defeat was bad. Now we must not lose faith in what we are doing. We have built a lot, but we were unable to find the goals," Stramaccioni told Sky Sport Italia.
"A defeat should not affect our work. [We were on] a fresh start in the second half, [but] Siena hit us. Now is the time to remain united. I have great confidence [in the players].
"We must not concede an inch. Today was the Inter who created more. Until the goal of Vergassola, Siena were only dangerous from corners. We are a new team, we have to find the right balance."
Inter travel to Chievo on Wednesday for their next Serie A fixture.