  Minifilaments are widespread small-scale structures in the solar atmosphere.
To better understand their formation and eruption mechanisms, we investigate
the entire life of a sigmoidal minifilament located below a large quiescent
filament observed by BBSO/GST on 2015 August 3. The H{\alpha} structure
initially appears as a group of arched threads, then transforms into two
J-shaped arcades, and finally forms a sigmoidal shape. SDO/AIA observations in
171{\AA} show that two coronal jets occur around the southern footpoint of the
minifilament before the minifilament eruption. The minifilament eruption starts
from the southern footpoint, then interacts with the overlying filament and
fails. The aforementioned observational changes correspond to three episodes of
flux cancellations observed by SDO/HMI. Unlike previous studies, the flux
cancellation occurs between the polarity where southern footpoint of the
minifilament is rooted in and an external polarity. We construct two magnetic
field models before the eruption using the flux rope insertion method, and find
an hyperbolic flux tube (HFT) above the flux cancellation site. The observation
and modeling results suggest that the eruption is triggered by the external
magnetic reconnection between the core field of the minifilament and the
external fields due to flux cancellations. This study reveals a new triggering
mechanism for minifilament eruptions and a new relationship between
minifilament eruptions and coronal jets.
