Ser ambicioso no es un defecto si también sabes trabajar en equipo.

Because Spanish can use an infinitive phrase as the subject of a sentence.

So ser ambicioso means to be ambitious / being ambitious, and the whole phrase acts as the subject:

• Ser ambicioso no es un defecto.
  = Being ambitious is not a flaw.

This is very common in Spanish:

• Fumar es malo. = Smoking is bad.
• Trabajar mucho cansa. = Working a lot is tiring.

Spanish often prefers this structure where English might also use being + adjective.

Because ser is used for qualities, characteristics, or more permanent descriptions, while estar is used for states or conditions.

Here, ambicioso describes a person’s character trait, so ser is the natural choice:

• ser ambicioso = to be ambitious as a trait
• estar ambicioso would sound unusual, because ambition is not normally treated as a temporary state in Spanish

So the sentence is talking about ambition as part of someone’s character, not a temporary mood.

Usually, yes, but the tone can vary a little depending on context.

In Spanish, ambicioso / ambiciosa can be:

• positive: driven, motivated, wanting to succeed
• slightly negative: overly eager for power, status, or success

In this sentence, the speaker is clearly using it in a more balanced way: being ambitious is not a flaw, as long as you also know how to work in a team.

So here it is close to English ambitious, with the same possible mix of positive and negative nuance depending on context.

Because the sentence is stated in a general way, and Spanish often uses the masculine singular as the default form in general statements.

So:

• Ser ambicioso no es un defecto... = a general statement
• Ser ambiciosa no es un defecto... = could be used if referring specifically to a woman or from a female perspective

This does not mean the sentence only applies to men. It is just the traditional default grammatical form.

Because defecto is a countable noun, and in this kind of sentence Spanish normally uses an article:

• Es un defecto = It is a flaw / a defect
• No es un defecto = It is not a flaw

Saying no es defecto would sound unnatural here.

In Spanish, articles are often used where English might leave them out.

Here si means if:

• ...si también sabes trabajar en equipo
  = ...if you also know how to work in a team

It has no accent because si = if.

Compare:

• si = if
• sí = yes

That accent mark is important because it changes the meaning.

Because también means also / too, and in Spanish it is very common to place it before the verb:

• si también sabes trabajar en equipo

Literally, this is something like:

• if you also know how to work in a team

Other placements are sometimes possible in Spanish, but this one is very natural and standard.

Saber + infinitive means to know how to do something.

So:

• sabes trabajar = you know how to work
• sabes trabajar en equipo = you know how to work in a team / work as part of a team

This is different from just knowing information. Compare:

• Sé la respuesta. = I know the answer.
• Sé conducir. = I know how to drive.

In this sentence, sabes trabajar en equipo means you have the ability or skill to do that.

Because Spanish often drops subject pronouns when the verb ending already shows who the subject is.

• sabes already means you know (informal singular)

So tú is not necessary.

You could say:

• si también sabes trabajar en equipo
• si tú también sabes trabajar en equipo

Both are possible, but without tú is more neutral and natural unless you want emphasis or contrast.

Trabajar en equipo is a very common expression meaning:

• to work in a team
• to work as part of a team
• to work collaboratively

The preposition en is just the normal one used in this fixed expression. You should learn trabajar en equipo as a chunk.

Examples:

• Es importante trabajar en equipo. = It’s important to work in a team.
• Sabe trabajar en equipo. = He/She knows how to work in a team.

Even though English often says work with others or work as a team, Spanish very naturally says trabajar en equipo.